The 25% chance is per egg, the more eggs you get the better your chance of hitting at least 1. The formula for the odds of hitting at least one homozygous from a pair of hets is 1 - 0.75^N where N is the number of eggs in the clutch. So if you can hatch a 6 egg clutch your chance of getting one or more homozygous is 82%. It never goes to 100% but the more eggs the better your chance.